Such integrated optical components are known, for example in Dannoux et al. U.S. Pat. No. 4,943,130 filed Mar. 12, 1987 and assigned to Corning Glass Works. Conforming to the preliminary specifications of specification T.W.NWT 000442 published in November 1990 by Bellcore (USA), such optical components must pass predetermined tests which assure the mechanical strength of the fiber/substrate attachment and the transmission quality of an optical signal. The mechanical strength is tested by a pulling force which is exerted upon the fiber/substrate attachment, and the attachment must resist a force of 5N across the temperature range from -40.degree. C. to +85.degree. C., or, further, in an atmosphere of 93% relative humidity at 60.degree. C., or, further, during aging for 2000 hours at 85.degree. C. Moreover, the excess signal loss observed for a transmitted optical signal must not exceed a predetermined threshold, for example, 0.8 dB for a component with one input and two outputs.
With the integrated optical components which are cited above one encounters a problem which is related to the different thermal expansions of the materials forming the substrate, the optical fibers and the adhesives of the assembly. The substrate is readily made of a glass which has a coefficient of thermal expansion on the order of 80.times.10.sup.-7 K.sup.-1. The integrated optical waveguide is formed in this glass by photolithographic masking and ion exchange, for example. The optical fiber, either single mode or multimode, comprises very pure silica and doped silica which have a coefficient of thermal expansion which is less than 6.times.10.sup.-7 K.sup.-1, for example. Thus, for the same temperature increase, the substrate is expanded more than the fiber, which fiber is attached to the substrate at two separated points. The substrate therefore exerts a tensile stress on the section of the fiber situated between these two points. This tensile force may generate a fiber fracture, a change in the optical properties of the silica which comprises the fiber, or a deterioration of the fiber attachment points. The coefficients of thermal expansion of the adhesive products used may also play an important role in the differential expansions which have been observed. Such phenomena can alter, and in some cases even destroy the optical continuity of the attachment between the fiber and the waveguide of the integrated optical component, and thus result in a concomitant alteration or even a complete loss of an optical signal transmitted across this attachment. Other causes of alteration of the attachment are the effects of environment, notably in humid atmosphere, and the aging of the materials comprising the component, especially in the event of excursions to decreasing temperatures, from ambient temperature toward low temperatures (-40.degree. C. for example).
The present invention has therefore as its aim the manufacture of an integrated optical component of the type described above and designed to insure satisfactory mechanical and optical characteristics across a predetermined wide range of temperature.
The present invention has also as its aim the manufacture of such a component having a satisfactory resistance to the effects of a high humidity atmosphere, and to the effects of aging.